FIG. 1 shows a circuit board assembly and a card edge connector of a prior technology. The circuit board assembly 100 includes a first circuit board 120, a second circuit board 140 and a coupling part 160. The first circuit board 120 includes printed circuit elements 122 and a connecting part 124. Various circuit elements are mounted on the printed circuit elements 122. The connecting part 124 includes tabs 126 which electrically connect the circuit elements on the printed circuit elements 122 to a first card edge connector 200. The tabs 126 can be formed on one side or both sides of the connecting part 124. The tabs 126 are usually plated with gold, and hence the connecting part 124 is called as a gold tab card edge. In the same manner as the first circuit board 120, the second circuit board 140 includes printed circuit elements 142 and a connecting part 144, and the connecting part 144 includes tabs 146. The coupling part 160 supports the first circuit board 120 and the second circuit board 140 in parallel, and is composed of a screw, a sleeve and a nut in the example shown in the FIG. 1. The first circuit board 120 is electrically connected to the second circuit board 140. The first card edge connector 200 includes an elongated aperture 220, and terminals 240 are arranged within the aperture 220. The second card edge connector 300 includes an elongated aperture 320, and terminals 340 are arranged within the aperture 320.
FIG. 2 shows a cross section of the card edge connector and the circuit board when these are connected. In the FIG. 2(A), the connecting part 124 of the first circuit board 120 moves toward the elongated aperture 220 of the first card edge connector 200, and the leading portion of the connecting part 124 is pressed against the terminals 240. Each of the terminals 240 is formed by a leaf spring, and the terminals 240 are in a closed condition in the FIG. 2(A).
In the FIG. 2(B), when the connecting part 124 of the first circuit board 120 is inserted toward a bottom of the aperture 220 by an applied force, the terminals 240 are opened, the tabs 126 slide on the terminals 240, and the connecting part 124 is further inserted toward the bottom of the aperture 220. When the leading portion of the connecting part 124 engages with the bottom of the aperture 220 or the portions of the both sides edges of the first circuit board 120 engage with the card edge connector 200, the connecting part 124 is stopped, and in this stopped condition, the tabs 126 are electrically connected to the terminals 240. Although the connection of the first circuit board 120 is shown in the FIG. 2 for simplifying the description, the same connecting operation as the above operation is made for the second circuit board 140.
In general, the force F1 required for moving the connecting part 124 of the circuit board to open the terminals 240, as shown in the FIG. 2(A), is larger than the force F2 required for sliding the connector part 124 on the opened terminals 240, as shown in the FIG. 2(B). Accordingly, the maximum value of the force required for simultaneously inserting the two connecting parts of the two circuit boards with the same shape of the circuit board assembly into the card edge connector is represented 2 F1.
The following two methods have been used for connecting a plurality of circuit boards of the circuit board assembly 100 to the card edge connectors 200 and 300.
(1) After that the first circuit board 120 is connected to the card edge connector 200 and the second circuit board 140 is connected to the card edge connector 300, the first and second circuit boards 120 and 140 are electrically and mechanically connected. and
(2) After that the first circuit board 120 and the second circuit board 140 are electrically and mechanically connected, both the circuit boards 120 and 140 are simultaneously connected to the card edge connectors 200 and 300, respectively.
Although a large force is not required to insert the respective circuit board into the card edge connector in the described method (1), it is necessary to electrically and mechanically connect both the circuit boards after the insertion of the respective circuit board into the card edge connector. This electrical and mechanical connection may prove to be difficult since the space between the circuit boards is narrow. Also, a more complicated mechanism is required to mechanically connect the circuit boards 120 and 140 in comparison with the described method (2), the method (1) is unfavorable in the size and the fabricating cost.
Although the assembling steps in the fabrication of the method (2) are relatively simple and the mechanism for mechanically coupling both the circuit boards is more simple than that of the method (1), the large force is required to simultaneously inserting the both the circuit boards into the card edge connectors. Therefore, the assembling work must be carefully made to prevent the problems that the large force causes the circuit boards to be distorted, so that solders are cracked, and the solders of the mounted circuit elements are peeled off.